EP1418195B1 - Method of manufacturing of a thermoplastic film using recycled plastics from bottles - Google Patents

Description

The invention relates to a process for producing a single or multilayer film by extrusion or coextrusion, biaxial orientation and thermosetting based on crystallizable thermoplastics whose main component is a crystallizable thermoplastic having a standard viscosity SV (DCE) of 600 to 1,000.

Biaxially oriented films of crystallizable thermoplastics are known and described in numerous ways. These films usually consist mainly of a polyester, in the production of accumulating Regenerat and additives that give the individual films the desired functionality. However, the raw material costs for the polyester are relatively high, so that sought after low-cost alternative starting materials for the production of the films.

In the EP-A 0 483 665 discloses a process for the treatment of thermally stressed polyester waste for reuse in the production of high-quality PET plastic articles, in which the molecular weight - and thus the SV value - of the melt is increased by post-condensation in the melt or in the solid phase.

From the US-A-5 503 790 For example, there is known a method of recycling PET waste into the manufacture of break-resistant and elastic PET articles. In this process, amorphous thermoplastic PET waste material is ground, mixed with solid, original PET, and the mixture is extruded into sheets. From the plates are then produced by a thermoforming process, for example by deep drawing, the desired moldings. That's for example Beverage cups or other articles intended for single use. Because the ground PET waste material has a reduced intrinsic viscosity, it can not be reused in the production of PET bottles.

Subject of the post-published, but prioritized senior EP-A 1 344 790 is a single or multilayer film based on a crystallizable polyester which contains at least one primary stabilizer in covalently bonded form. The inherent in the film production Regenerat can be used again in production in larger quantities.

It was therefore an object to provide a method for producing single or multilayer thermoplastic films available that manages with cheaper materials. The films produced after that should nevertheless have the positive properties of the known films. This includes in particular a high viscosity.

This object is achieved by a method in which a significant proportion of a resulting in the bottle industry as waste or by-product crystallizable thermoplastics is used with a relatively high viscosity.

The invention accordingly provides a process for producing a single-layer or multi-layer film based on crystallizable thermoplastics whose main component is a crystallizable thermoplastic having a standard viscosity SV (dichloroacetic acid, DCE) of 600 to 1,000, by extrusion or coextrusion, biaxial orientation and thermofixing, characterized in that the thermoplastic is a crystallizable polyester blended prior to extrusion or co-extrusion with a blend of regenerate inherent in film making and up to less than 50% by weight, based on the total weight of all thermoplastics, of a secondary Thermoplastics with a standard viscosity SV (DCE) of more than 900 to 1,500, which is also a crystallizable polyester is provided that the standard viscosity SV (DCE) of the thermoplastic used as the main component is different from that of the secondary thermoplastic by at least 100 units, with enough of the secondary thermoplastic added that the calculated standard viscosity SV (DCE) of the mixture of the inherent accumulating regenerate and the secondary thermoplastic is practically equal to that of the thermoplastic used as the main component, wherein the standard viscosity SV (DCE) on a 1 wt .-% solution in dichloroacetic acid (DCE) at 25 ° C is measured.

The main constituent of both crystallizable thermoplastics are in a preferred embodiment polycondensates of aromatic dicarboxylic acids, especially terephthalic acid, isophthalic acid and / or naphthalene-1,6- or 2,6-dicarboxylic acid, and aliphatic (C ₂ -C ₁₀ ) glycols, especially ethylene glycol or cyclohexane 1,4-diyldimethanol. These are, in particular, polyethylene terephthalate, polybutylene terephthalate, poly (cyclohexanediyl-1,4-dimethylene terephthalate), poly (ethylene naphthalene-2,6-dicarboxylate) or polyethylene naphthalate / bibenzoate. In the polycondensates are usually 100 to 10,000 ppm of stabilizers condensed.

The crystallizable thermoplastic, which is also referred to as the original or primary raw material, preferably consists of crystallisable polyester, in particular of crystallisable polyethylene terephthalate, of crystallisable polyethylene naphthalate (PEN) or of a mixture thereof. The thermal degradation behavior of the original raw material is optionally optimized by condensing stabilizers into the polymer chain.

The term "crystallisable polyesters" is understood to mean crystallizable homo- and copolymers, crystallizable compounds, crystallizable recyclates and other variations of the crystallizable thermoplastics. The standard viscosity SV (DCE) of the crystallizable thermoplastic used as the original raw material is generally from 600 to 1000, preferably from 700 to 980.

The preparation of the polyester can both by the transesterification (DMT process), z. Example, with the aid of transesterification catalysts such as Zn, Mg, Ca, Mn, Li or Ge salts, as well as by the direct esterification process (PTA process) carried out in the various polycondensation catalysts, such as Sb-, Ge, Al or Ti compounds, and phosphorus compounds are used as stabilizers, with Sb and Ti compounds are preferred as polycondensation catalysts.

The copolyesters can contain up to 50 mol%, in particular up to 30 mol%, of comonomer units, variation in the glycol component and / or the acid component being possible. Suitable comonomers for the acid component are, for example, 4,4'-bibenzoic acid, adipic acid, glutaric acid, succinic acid, sebacic acid, phthalic acid, 5-Na-sulfoisophthalic acid or polyfunctional acids, such as trimellitic acid.

The further crystallizable thermoplastic (also referred to below as secondary raw material or secondary thermoplastic) is obtained especially in the plastic bottle industry as a by-product or waste product and as a recyclate. It is inexpensive and available in large quantities, but has not been used to make biaxially oriented films. The said use is also new and part of the present invention.

The secondary thermoplastic is used in a proportion of preferably 5 to 45% by weight, particularly preferably 10 to 40% by weight. Suitably, it is also a crystallizable polyester. The standard viscosity SV (DCE) of the secondary thermoplastic is preferably from 1,000 to 1,400, particularly preferably from 1,050 to 1,300. With a standard viscosity SV (DCE) of more than 1,500, it often results in the production of gels, specks and reduced filter life. At viscosities of less than 900, the use of such materials offers no other benefits besides the lower price. The secondary thermoplastic can be in the form of ground or on others Be used shredded preforms or unused bottles from the bottle industry ("preform regrind" or "post-industrial" granules), or in the form of already recycled preform regrind. After use, cleaned and ground or otherwise sufficiently comminuted plastic bottles ("post-consumer" material) are also suitable as starting material for the process according to the invention. All these materials are compared to the original polyester raw materials significantly cheaper in price, which makes the film production economically favorable.

Preferably, the secondary thermoplastic is added via the recirculation loop, i. is mixed with the regenerated material inherent in film production (by blending, etc.) and recycled to production. The regenerate has a reduced standard viscosity compared to the original raw material. The higher-viscosity secondary raw material is therefore expediently metered in such an amount that the viscosity of the mixture practically corresponds to that of the original raw material.

The secondary raw material should have a copolyester content of less than 10% by weight. Higher copolyester contents can have a disruptive effect on the film production and / or adversely affect the film properties. Furthermore, it should not contain any color additives or pigments, since these have a disturbing effect on the production of transparent and colored films.

The polyester film produced from these raw materials can be single-layered or multi-layered. In the multi-layered embodiment, it is made up of at least one core layer and at least one cover layer, wherein in particular a three-layered ABA or ABC structure is preferred. The films produced according to the invention can be constructed symmetrically or asymmetrically, with different polyesters or those of the same chemical composition optionally also provided with additional additives, but can be combined with different molecular weight and viscosity by coextrusion.

In the multilayered embodiment, the core layer preferably consists of a mixture of the original raw material, regenerated material and secondary raw material or of a mixture of original raw material and regenerated material, wherein the regenerated material was produced from a mixture of inherently incurred film waste and secondary raw material. The cover layers of the multilayer film may consist, for example, of polyethylene terephthalate homopolymers, of polyethylene naphthalate homopolymers or of polyethylene terephthalate-polyethylene naphthalate copolymers or compounds.

Base layer and / or outer layer (s) may additionally contain other conventional additives, such as antiblocking agents, soluble dyes, white and / or colored pigments. They are expediently added to the polymer or the polymer mixture before melting.

As additives it is also possible to choose mixtures of two or more different antiblocking agents or mixtures of antiblocking agents of the same composition but different particle size. The particles may be added to the individual layers in the usual concentrations, e.g. as a glycolic dispersion, during polycondensation or via masterbatches during extrusion. Pigment proportions of from 0.0001 to 10.0% by weight, based on the weight of the layers, have proved to be particularly suitable.

The film can also be UV-stabilized, flame-retardant, sealable, coated on one or both sides, hydrolysis-stabilized, equipped with antioxidants, chemically pretreated, corona-treated and / or flame-treated by addition of suitable additives.

In a particular embodiment, at least one inorganic white pigment and / or at least one inorganic colored pigment is added during the production of the film, which then becomes part of the base layer and / or, if appropriate, of the cover layer. The inorganic pigment is preferably metered in via masterbatch technology, but can also be incorporated directly at the raw material manufacturer. The proportion of the inorganic pigment is generally 0.2 to 40 wt .-%, preferably 0.3 to 25 wt .-%, each based on the weight of the thermoplastic of the thus equipped layer.

Suitable white pigments are preferably titanium dioxide, barium sulfate, calcium carbonate, kaolin, silica, with titanium dioxide (anatase or rutile) and barium sulfate being preferred.

Titanium dioxide of the type described does not give rise to any vacuoles during the film production within the polymer matrix.

The optionally used titanium dioxide particles may have a coating of inorganic oxides commonly used as a coating for TiO ₂ white pigment in papers or paints to improve light fastness.

TiO ₂ is known to be photoactive. When exposed to UV rays, free radicals form on the surface of the particles. These free radicals can migrate to the film-forming polymers, resulting in degradation reactions and yellowing. Particularly suitable oxides include the oxides of aluminum, silicon, zinc or magnesium or mixtures of two or more of these compounds. TiO ₂ particles with a coating of several of these compounds are z. B. in the EP-A 0 044 515 and EP-A 0 078 633 described. Furthermore, the coating may contain organic compounds with polar and nonpolar groups. The organic compounds must be sufficiently thermostable in the production of the film by extrusion of the polymer melt.

Polar groups are, for example, -OH; -OR; --COOX; (X = R; H or Na, R = (C ₁ -C ₃₄ ) alkyl). Preferred organic compounds are alkanols and fatty acids having 8 to 30 carbon atoms in the alkyl moiety, especially fatty acids and primary n-alkanols having 12 to 24 carbon atoms, and polydiorganosiloxanes and / or polyorganohydrogensiloxanes, such as polydimethylsiloxane and polymethylhydrogensiloxane.

The coating of titanium dioxide particles usually consists of 1 to 12 g, especially 2 to 6 g, inorganic oxides and 0.5 to 3 g, in particular 0.7 to 1.5 g, organic compounds, each based on 100 g of titanium dioxide. The coating is applied to the particles in aqueous suspension. The inorganic oxides are selected from water-soluble compounds, e.g. As alkali, especially sodium nitrate, sodium silicate (water glass) or silica precipitated in the aqueous suspension.

Under inorganic oxides such as Al ₂ O ₃ or SiO ₂ , the hydroxides or their various dewatering stages such. B. oxide hydrate without recognizing their exact composition and structure. On the TiO ₂ pigment are after annealing and grinding in aqueous suspension, the oxide hydrates z. As the aluminum and / or silicon, the pigments are then washed and dried. This precipitation can thus be done directly in a suspension, as obtained in the manufacturing process after the annealing and the subsequent wet grinding. The precipitation of the oxides and / or oxide hydrates of the respective metals is carried out from the water-soluble metal salts in the known pH range, for the aluminum, for example, aluminum sulfate in aqueous solution (pH less than 4) is used and by addition of aqueous ammonia solution or sodium hydroxide in the pH range between 5 and 9, preferably between 7 and 8.5, precipitates the oxide hydrate. Assuming a water glass or alkali aluminate solution, the pH of the TiO ₂ suspension should be in the strongly alkaline range (pH greater than 8). The precipitation is then carried out by adding mineral acid such as sulfuric acid in pH range 5 to 8. After the precipitation of the metal oxides, the suspension is stirred for a further 15 minutes to about 2 hours, during which time the precipitated layers undergo aging. The coated product is separated from the aqueous dispersion and after washing at elevated temperature, especially at 70 to 100 ° C, dried.

In another embodiment, barium sulfate is preferred as the pigment, wherein the concentration of the pigment is preferably between 0.2 wt .-% and 40 wt .-%, in particular between 0.3 wt .-% and 25 wt .-%, based on the Weight of crystallizable thermoplastic, lies. Preferably, the barium sulfate is added via the so-called masterbatch technology directly in the film production.

In the case of pigmentation with barium sulfate, the film additionally contains at least one optical brightener which is present in a proportion of from 10 ppm to 50,000 ppm, preferably from 20 ppm to 30,000 ppm, more preferably from 50 ppm to 25,000 ppm, in each case based on the weight of the crystallisable Thermoplastics, is used. Preferably, it is added via the so-called masterbatch technology directly in the film production. Suitable are benzoxazole derivatives, triazines, phenylcoumarins and bis-styrylbiphenyls. Preference is given to using ®Tinopal (Ciba-Geigy, Basel, Switzerland), ®Hostalux KS (Clariant, Germany) and ®Eastobrite OB-1 (Eastman). The optical brightener is able to absorb UV rays in the range of 360 to 380 nm and release it as a longer-wavelength, visible blue-violet light.

In addition to the optical brightener also soluble blue dyes can be added. Ultramarine blue and anthraquinone dyes, in particular Sudan blue 2 (BASF, Ludwigshafen, Federal Republic of Germany), are suitable for this purpose. The blue dyes are particularly preferred in a proportion of from 10 ppm to 10,000 ppm, preferably from 20 ppm to 5,000 ppm 50 ppm to 1,000 ppm, in each case based on the weight of the crystallizable thermoplastic used.

In a preferred embodiment, precipitated barium sulfate types are used. Precipitated barium sulphate is obtained from barium salts and sulphates or sulfuric acid as finely divided colorless powder whose grain size can be controlled by the precipitation conditions. Precipitated barium sulfates can be prepared by the conventional methods described in Kunststoff-Journal 8, No. 10, 30-36 and No. 11, 36-31 (1974). The proportion of barium sulfate is advantageously from 0.2 to 40 wt .-%, preferably 0.3 to 25 wt .-%, particularly preferably 1 to 25 wt .-%, each based on the weight of the thermoplastic. The mean particle size is relatively small and is preferably in the range of 0.1 to 5 microns, more preferably in the range of 0.2 to 3 microns. The density of the barium sulfate used is between 4 and 5 g / cm ³ .

In a particularly preferred embodiment, the film produced according to the invention contains as main constituent a crystallizable polyethylene terephthalate and 1 wt .-% to 25 wt .-% precipitated barium sulfate, suitably having a particle diameter of 0.4 to 1 .mu.m, Blanc fixed XR-HX or Blanc fixed HXH from Sachtleben Chemie is particularly preferred.

Furthermore, the film produced according to the present invention preferably contains 10 to 50,000 ppm of an optical brightener which is soluble in the crystallizable thermoplastic, with triazine phenylcoumarin (®Tinopal, Ciba-Geigy, Basel, Switzerland), ®Hostalux KS and ®Eastobrite OB-1 (Eastman) are particularly preferred.

In a further embodiment, the film produced according to the invention can also be colored in color. The film of this embodiment may have in the base and / or the overcoat layers an inorganic color pigment, inorganic Black pigments and inorganic or organic colored pigments. The pigment is preferably added via the masterbatch technology, but can also be incorporated directly at the raw material manufacturer. The proportion of pigment is generally 0.2 to 40 wt .-%, preferably 0.3 to 25 wt .-%, each based on the weight of the crystallizable thermoplastic.

Typical inorganic black pigments are carbon black modifications which may also be coated, carbon pigments which differ from the carbon black pigments by a higher ash content, and black oxide pigments such as iron oxide black and copper, chromium or iron oxide mixtures (mixed phase pigments).

Suitable inorganic colored pigments are oxidic colored pigments, hydroxyl-containing pigments, sulfidic pigments and chromates. Examples of oxidic colored pigments are iron oxide red, titanium oxide-nickel oxide-antimony oxide mixed phase pigments, titanium dioxide chromium oxide, antimony oxide mixed phase pigments, mixtures of the oxides of iron, zinc and titanium, chromium oxide iron oxide brown, spinels of the system cobalt-aluminum-titanium-nickel Zinc oxide and mixed phase pigments based on other metal oxides. Typical hydroxyl-containing pigments are, for example, oxide hydroxides of trivalent iron, such as FeOOH. Examples of sulfidic pigments are cadmium sulfide selenides, cadmium zinc sulfides, sodium aluminum silicate with polysulfide-bonded sulfur in the lattice. Examples of chromates are bleach chromates, which can be present in the crystal forms monoclinic, rhombic and tetragonal. All colored pigments, like the white and black pigments, can be present both uncoated and inorganic and / or organically coated.

The organic pigments are usually divided into azo pigments and so-called non-azo pigments. Characteristic of the azo pigments is the azo (-N = N -) group. Azo pigments may monoazo pigments, diazo pigments, Diazo condensation pigments, salts of azo dye acids and mixtures of the azo pigments.

In another embodiment, the film is colored so that it is transparent. In general, a dye soluble in the thermoplastic is used for this purpose. The solubility of the dye is determined according to DIN 55 949. Its proportion is suitably from 0.01 to 20.0 wt .-%, preferably 0.05 to 10.0 wt .-%, each based on the weight of the crystallizable thermoplastic. The transparent coloration of the film is due to a wavelength-dependent absorption of the light by the molecularly dissolved dye in the thermoplastic. Particularly suitable are fat-soluble or aromatic-soluble dyes, for example azo or anthraquinone dyes. They are particularly suitable for coloring PET, since its high glass transition temperature Tg, the migration of the dye is limited. Suitable soluble dyes are also C.I. Solvent Yellow 93 (a pyrazolone derivative), C.I. Solvent Yellow 16 (a fat-soluble azo dye), Fluorolgreen Gold (a fluorescent polycyclic dye), C.I. Solvent Red 1 (an azo dye), azo dyes such as Thermoplastrot BS, Sudan Red BB, C.I. Solvent Red 138 (an anthraquinone derivative), fluorescent benzopyran dyes such as Fluorol Red GK and Fluorol orange GK, C.I. Solvent Blue 35 (an anthraquinone dye), C.I. Solvent Blue 15: 1 (a phthalocyanine dye) and mixtures thereof. The coloration with the soluble dyes is referred to as transparent, translucent or translucent.

The soluble dye is preferably added via the masterbatch technology during film production, but can also be incorporated during the production of the raw material. The proportion of soluble dyes is generally 0.01 to 40.0 wt .-%, preferably 0.05 to 25, O wt .-%, each based on the weight of the crystallizable thermoplastic.

Due to the drying of the polymers used and the extrusion process, a viscosity reduction of the polymer takes place. The viscosity of the Production process used Regenerates, which is produced from inherent accumulation of foil in a subsequent extrusion step, is naturally lower than the viscosity of the original raw material used by the additional extrusion step.

wobei

SV_OR =

mittlerer SV-Wert aller Rohstoffe gemäß Originalrohstoff

Δ_R =

SV-Wert-Abbau durch Extrusionsschritt beim Regenerieren

SV_VER =

SV-Wert des eingesetzten Verschnitts bzw. SV-Wert der hergestellten Folie

SV_FL =

SV-Wert des Sekundär-Thermoplasten

bedeuten. Durch die Verwendung einer kostengünstigen hochviskosen Rohstoffkomponente ist es darüber hinaus möglich, den Regeneratanteil bei der Herstellung auch solcher Folien deutlich zu erhöhen, bei denen bedingt durch den hohen Viskositätsabbau bei der Verarbeitung der Regeneratanteil sonst begrenzt ist.During subsequent reuse, this can lead to viscosity fluctuations that reduce process stability. This is prevented in the process according to the invention in that the amount of highly viscous secondary thermoplastic is added to the film blend in the regeneration process, which is necessary to raise the viscosity to the initial level. If this amount is added to the regenerating cycle, the optimum proportion of the second thermoplastic can be easily calculated using the following formula: $$\mathrm{secondary}\ddot{\mathrm{a}}\mathrm{r}\mathrm{-}\mathrm{thermoplastic}\mathrm{=}\left(\left({\mathrm{SV}}_{\mathrm{OR}}\mathrm{+}{\mathrm{\Delta }}_{\mathrm{R}}\mathrm{-}{\mathrm{SV}}_{\mathrm{VER}}\right)\mathrm{/}\left({\mathrm{SV}}_{\mathrm{FL}}\mathrm{-}{\mathrm{SV}}_{\mathrm{VER}}\right)\right)\mathrm{*}\mathrm{100}\mathrm{.}$$

in which

SV _OR =

mean SV value of all raw materials according to original raw material

Δ _R =

SV value reduction by extrusion step during regeneration

SV _VER =

SV value of the used blend or SV value of the produced film

SV _FL =

SV value of the secondary thermoplastic

mean. By using a low-cost, highly viscous raw material component, it is also possible to significantly increase the amount of regenerate in the production of such films in which due to the high viscosity reduction during processing of the regenerated content is otherwise limited.

Surprisingly, the secondary thermoplastic in a proportion of up to less than 50 wt .-%, based on the total weight of all thermoplastics, can be used without gelation occurs or that specks or other Surface defects occur. Also surprisingly, the filter life compared to conventional film recipes remain unaffected.

The film can be oriented excellently in its production both in the longitudinal and in the transverse direction without breaks. The oriented (= stretched) film generally has a thickness of 0.9 to 500 .mu.m, preferably from 5 to 350 .mu.m, particularly preferably from 10 to 300 .mu.m.

When using the secondary thermoplastic in a proportion of 20 to less than 50 wt .-%, the mechanical properties may initially deteriorate. By adapting the process parameters, in particular the stretching ratios and the stretching temperatures, however, the desired properties can be restored.

Among the good mechanical properties are, among others, a high modulus of elasticity (in the longitudinal direction = machine direction (MD) greater than 3,200 N / mm ² , preferably greater than 3,500 N / mm ² , in the transverse direction (TD) greater than 3,500 N / mm ² , preferably greater than 3,800 N / mm ² , in each case determined according to ISO 527-1-2), and good tensile strength values (in MD more than 100 N / mm ² , in TD more than 130 N / mm ² ).

The secondary thermoplastic often contains a certain percentage of isophthalic acid (IPA), which can negatively affect the durable heat resistance of the PET film. For films which have to have a high long-term heat resistance, the use of 2 to a maximum of 25% by weight of IPA-containing secondary thermoplastic makes sense.

Furthermore, it was more than surprising that the films produced can be thermoformed excellent without additional additives. Thermoformability means that the film on commercial thermoforming machines without deep drawing or thermoforming unprofitable predrying into complex and large-area moldings.

The polyester films can by known methods, optionally with other raw materials and / or other conventional additives in conventional amounts (0.1 to 30 wt .-%, based on the weight of the film) both as single or multi-layer, optionally coextruded films with the same or differently formed surfaces, wherein one surface contains, for example, particles and the other does not or all layers contain particles. Likewise, one or both surfaces of the film may be provided with a functional coating by known methods.

The secondary thermoplastic should, like the original raw material, be pre-crystallized or pre-dried. This predrying comprises a gradual heating, preferably under reduced pressure (20 to 80 mbar, preferably 30 to 60 mbar, in particular 40 to 50 mbar) and with stirring and, if appropriate, subsequent drying at a constant, elevated temperature, likewise preferably under reduced pressure. The polymers are preferably charged at room temperature from a dosing tank in the desired mixture with optionally other raw material components batchwise in a vacuum dryer, which during the drying or residence time a temperature range of 10 ° C to 160 ° C, preferably 20 ° C to 150 ° C. , in particular 30 ° C to 130 ° C passes. During the approximately six-, preferably five, in particular four-hour residence time, the raw material mixture is stirred at 10 to 70 rpm, preferably 15 to 65 rpm, in particular 20 to 60 rpm. The thus pre-crystallized or predried raw material mixture is in a downstream, also evacuated container at 90 ° C to 180 ° C, preferably 100 ° C to 170 ° C, in particular 110 ° C to 160 ° C for 2 to 8 hours, preferably 2 to 7 hours, in particular 4 to 6 hours after-dried.

In the preferred extrusion process for producing the film, the molten polymer material with the additives is extruded through a slot die and quenched as a largely amorphous prefilm on a chill roll. This film is then reheated and stretched in the longitudinal and transverse direction or in the transverse and longitudinal direction or in the longitudinal, in the transverse and again and in the longitudinal direction and / or transverse direction. The stretching temperatures are generally T _G + 10 ° C to T _G + 60 ° C (T _G = glass transition temperature of the film), the draw ratio of the longitudinal stretching is usually from 2 to 6, in particular from 3 to 4.5, that of the transverse extent at 2 to 5, in particular at 3 to 4.5 and that of the possibly performed second longitudinal and transverse extension at 1.1 to 5. The first longitudinal stretching may optionally be carried out simultaneously with the transverse extension (simultaneous stretching). This is followed by the heat-setting of the film at oven temperatures of 180 to 260 ° C, in particular 220 to 250 ° C. Subsequently, the film is cooled and wound.

It was surprising that a film with the required property profile could be produced economically and without adhesive bonding in the dryer by predrying or pre-crystallization. Also, the yellow value of the film was not adversely affected compared to a conventionally produced film within the measurement accuracy.

Furthermore, it was surprising that the regenerated material can also be used again without negatively influencing the yellowness of the film.

Due to the combination of excellent properties, the film produced according to the invention is outstandingly suitable for a variety of applications, for example for cable and motor insulation, thermal transfer films, interior trim, trade fair construction and trade show products, as displays, for signs, protective glazing of machines and vehicles Lighting sector, in shop and shelf construction, as promotional items or laminating medium and much more.

If the materials used comply with the valid legal requirements, the films produced from them can also be used as packaging material even in the food industry.

All these films are easily recyclable without polluting the environment.

The measurements of the individual properties are carried out according to the following standards or procedures:

yellowness

The yellow value (YID) is the deviation from the colorlessness in the direction "yellow" and was measured according to DIN 6167.

Light transmission (transparency)

Under the light transmission is the ratio of the total transmitted light to the amount of incident light to understand.

cloudiness

Turbidity is the percentage of transmitted light that differs by more than 2.5 ° from the incident light beam. The image sharpness was determined at an angle smaller than 2.5 °.

Light transmission and turbidity were measured with the measuring device "®HAZEGARD plus" (Byk Gardener, Germany) according to ASTM D 1003.

surface defects

The surface defects were determined visually.

Term thermal stability

The measurement of the continuous heat resistance was based on IEC216.

Instead of using the tensile strength recommended in the standard, 2% elongation at break was chosen as the failure criterion. The temperatures selected for annealing were 150 ° C, 160 ° C, 170 ° C and 180 ° C.

Mechanical properties

Modulus of elasticity and tear strength were measured in the longitudinal and transverse directions according to ISO 527-1-2.

Standard Viscosity (SV) and Intrinsic Viscosity (IV):

The standard viscosity SV was - based on DIN 53726 - measured as 1gew.% Solution in dichloroacetic acid (DCE) at 25 ° C. SV (DCE) = (η _rel -1) x 1000. The intrinsic viscosity (IV) was calculated from the standard viscosity as follows $$\mathrm{IV}\left(\mathrm{DCE}\right)=6.67\times {10}^{-4}\mathrm{SV}\left(\mathrm{DCE}\right)+0.118$$

Examples

The invention is explained in more detail below with reference to examples and comparative examples. It describes the production of single or multilayer films of different thicknesses in an extrusion line. Percentages are by weight unless otherwise stated or obvious from the context.

example 1

A 190 μm thick white monofilm was produced from: 34% M04 (PET clear raw material from KoSa, Germany with an SV value of 980), 6% A masterbatch containing, in addition to PET, 4% by weight of titanium dioxide and 3% by weight of calcium carbonate and having an SV of 810, 60% Regenerat, which consisted of 60% inherently incurred film waste and 40% bottle recycling (Post-Industrial, PET-A, Texplast, Germany) with an SV value of 1,200.

The film blend used had an SV of 850, resulting in a calculated blend SV of 990 for the material used prior to regeneration. As a result of the extrusion step during the regeneration, the SV value of the mixture was reduced by 40 units to an SV value of 950, with the SV value of the regenerate having approximately the same SV value as the sum of the original raw materials.

The film made according to this recipe had an SV of about 850.

The overall yield in the production of this film (= proportion of salable film to extrudate used) was 64%, ie. 36% of the extrudate again occurred as a blend. Under these conditions, the raw materials cycle was closed (60% reclaim with 60% blend content corresponds to a total blend content of 36%).

Example 2

A 4.5 μm thick monofilm was produced from: 20% RT49 (PET clear raw material from KoSa, Germany with an SV value of 810), 10% Masterbatch with an SV value of 810, which in addition to PET 1% silicon dioxide (Sylobloc, Grace, Germany) contained, and 70% Regenerat, which consisted of 82% inherent foil waste and 18% bottle recycling (Post-Industrial, PET-A, Texplast, Germany) with an SV value of 1,200.

The film blend used had an SV value of 750, resulting in a calculated blend SV of 831 for the material used prior to regeneration. As a result of the extrusion step during regeneration, this compound SV value decreased by about 20 units to an SV value of 810, whereby the SV value of the regenerate had approximately the same SV value as the sum of the original raw materials.

Example 3

A 12 μm thick ABA film was produced as follows:
Cover layers per 1 μm thick): 90% RT49 (PET clear raw material from KoSa, Germany with an SV value of 810) 10% Masterbatch with an SV value of 810, which in addition to PET 1% silica (Sylobloc, Grace, Germany) contained.
Base layer (10 μm thick): 40% RT49 (PET clear raw material from KoSa, Germany with an SV value of 810) and 60% Regenerat, which consisted of 86% inherently incurred film waste and 14% bottle recycling (Post-Industrial, PET-A, Texplast, Germany) with an SV value of 1,200.

The film blend used had an SV value of 770, resulting in a calculated blend SV of 830 for the material used prior to regeneration. As a result of the extrusion step during regeneration, this mixing SV value was reduced by about 20 units to an SV value of 810, whereby the SV value of the regenerate had approximately the same SV value as the sum of the original raw materials.

Example 4

Analogously to Example 2, a 4.5 micron thick monofilm was prepared from: 20% RT49 (PET clear raw material from KoSa, Germany with an SV value of 810), 10% Masterbatch with an SV value of 810, which in addition to PET contained 1% by weight of silicon dioxide (Sylobloc, Grace, Germany), 57% Regenerate made from inherent film waste, as well as 13% Bottle recycling (Post-Industrial, PET-A, Texplast, Germany) with an SV value of 1,200.

Also in this example bottle recycle was added to increase the SV value, but not via the recirculation cycle. The homogeneity of the polymer melt was thereby somewhat reduced. This embodiment is therefore less preferred.

Comparative Example 1

Example 1 was repeated, but now without the use of bottle recycle. In order to achieve an SV value of the film of 850 with otherwise identical properties, the following recipe was required: 81% M04 (PET clear raw material from KoSa, Germany with an SV value of 980), 9% Masterbatch, which in addition to PET 4 wt .-% titanium dioxide and 3 wt .-% calcium carbonate and which had an SV value of 810 and 10% Regenerate, which consisted of inherently incurred foil waste.

The mixture SV of the formulation was similar to Example 1 about 950. The SV value degradation during drying and extrusion for film production was about 100 SV value units, so that the SV value of the film was 850.

The viscosity of the original raw material, masterbatch and regenerate was very different, which drastically reduced the homogeneity of the polymer melt.

With an overall yield of 64% in film production, only 10% of film wastage could be traced back here, which made film production uneconomic.

The properties of the films are shown in the following table: <B> Table </ b> properties B1 B2 B3 B4 VB1 thickness [.Mu.m] 190 4.5 12 4.5 190 yellowness 17 1.2 1.2 1.2 17 transparency [%] 59 91 91 91 59 cloudiness [%] - 9 1.7 9 - tear strength along [N / mm ² ] 200 310 250 310 205 crosswise [N / mm ² ] 230 250 260 250 230 elongation at break along [%] 200 80 110 85 210 crosswise [%] 130 100 100 100 130 Modulus along [N / mm ² ] 3900 5100 4200 5100 4000 crosswise [N / mm ² ] 4300 4300 5000 4250 4350 surface defects none none none none none Term thermal stability Good Good Good Good Good Raw material cycle closed Yes Yes Yes Yes No Homogeneity of the polymer melt Good Good Good sufficient Good

Claims (12)

1. A process for producing a single-layer or multilayer film based on crystallizable thermoplastics whose principal constituent is a crystallizable thermoplastic having a standard viscosity SV (dichloroacetic acid, DCA) of from 600 to 1 000, by extrusion or coextrusion, biaxial orientation, and heat setting, which comprises the thermoplastic being a crystallizable polyester which is mixed, prior to extrusion or coextrusion, with a mixture consisting of

   - regrind arising during film production and

   - up to less than 50 % by weight, based on the total weight of all thermoplastics, of a secondary thermoplastic having a standard viscosity SV (DCA) of more than 900 to 1 500, which is likewise a crystallizable polyester,

   with the proviso that the standard viscosity SV (DCA) of the thermoplastic used as principal constituent differs from that of the secondary thermoplastic by at least 100 units, the amount added of the secondary thermoplastic being such that the arithmetically determined standard viscosity SV (DCA) of the mixture of the production regrind and the secondary thermoplastic is virtually the same as that of the thermoplastic used as principal constituent, the standard viscosity SV (DCA) being measured on a 1 % strength by weight solution in dichloroacetic acid (DCA) at 25 °C.
2. The process as claimed in claim 1, wherein the crystallizable thermoplastic used as principal constituent has a standard viscosity SV (DCA) of from 700 to 900.
3. The process as claimed in claim 1 or 2, wherein the secondary thermoplastic has a standard viscosity SV (DCA) of from 1 000 to 1 400, preferably from 1 050 to 1 300.
4. The process as claimed in one or more of claims 1 to 3, wherein the fraction of the secondary thermoplastic is from 5 to 45 % by weight, preferably from 10 to 40 % by weight, based in each case on the total weight of all crystallizable thermoplastics.
5. The process as claimed in one or more of claims 1 to 4, wherein the crystallizable thermoplastics are polyesters or copolyesters.
6. The process as claimed in claim 5, wherein the secondary thermoplastic contains less than 10 % by weight of copolyesters.
7. The process as claimed in claim 5, wherein the polyester is a polycondensate of an aromatic dicarboxylic acid, preferably terephthalic acid, isophthalic acid and/or naphthalene-2,6-dicarboxylic acid, and an aliphatic diol having from 2 to 10 carbon atoms, preferably ethylene glycol.
8. The process as claimed in claim 1, wherein the regrind arising during film production is recycled to the production stage via a regrind circuit.
9. The process as claimed in claim 1, wherein the regrind arising during film production, mixed with the secondary thermoplastic, is added via the regrind circuit.
10. The process as claimed in one or more of claims 1 to 9, wherein after orientation and heat setting the film has a thickness of from 0.9 to 500 µm, preferably from 5 to 350 µm, more preferably from 10 to 300 µm.
11. The process as claimed in one or more of claims 1 to 10, wherein the film is UV-stabilized by addition of additives, made flame retardant, sealable, coated on one or both sides, stabilized with respect to hydrolysis, treated with antioxidants, chemically pretreated, corona-treated and/or flame-treated.
12. The process as claimed in claim 1 to 11, wherein, as secondary thermoplastic, use is made of a crystallizable thermoplastic which has a standard viscosity SV (DCA) of more than 900 to 1 500 and which originates from the production of plastic bottles or from recycled plastic bottles.